Usually, spacers of an insulating glass unit comprising two or more glass panes consist of hollow aluminum or steel profiles.
From DE-A-30 02 904 a spacer in form of a strip of a rectangular cross section is known, which strip is already often known as a “swiggle strip” and, provided with protective films, comes from a storage drum or hasp and is applied onto the glass pane by means of an apparatus equipped with a turning head. Said strip-like spacer on the basis of butyl caoutchouc is viscoplastic, strongly adhesive (which is desirable for achieving a gas-tight connection at first between the first and later the second glass pane of the insulating glass unit) and has a strongly temperature-dependent viscosity.
Recently, substantially less temperature-sensitive elastoplastic spacer strips, presumably on the basis of polyurethane, have been developed which also show a rectangular cross section, are substantially more stable with respect to shape and dimension than the so-called “swiggle strip”, comprise on the later outside a lamination made of aluminum foil and are provided only on the two narrow sides intended for the gluing with the glass panes with a thin adhesive and sealing layer which is covered until the application with protective foils.
Up until now these elastoplastic spacer strips were placed by hand on the first glass pane and, if necessary, corner miters were punched out. In the case of a mechanical application with an apparatus of the kind known from DE A 37 26 274 for example it has been noticed that the corners of the spacer will break in or are pressed outwardly towards the edge of the glass pane. It may also occur that the location of the joint between the start and end of the strip will open or the long straight section may go wavy. The cause of these problems is seen by the fact that the spacer strip is not applied at a constant speed. Rather, the application starts at speed zero, reaches a maximum value, is equal zero in the first corner again, rises again up to the next corner, etc. That is why it was presumed at first that the mentioned unsatisfactory work results were caused by the difficulties in synchronizing the movements of the numerous intermittently working drives of such an apparatus.
The invention is based on the object of providing a method and an apparatus which allow a clean, dimensionally-precise application of spacer strips.
This object is achieved with respect to the method by the invention by the following steps:                Unwinding of the strip from a storage drum without any tensile stress and with at least a linear speed corresponding at least on the average to the application speed;        Supplying the strip to the application point in a manner free from any tensile or shearing stress.        
The invention is based on the finding that the quality defects observed when using respectively modified known apparatuses for applying plastic spacer strips are not caused by the electric control of the apparatus, i.e. the control unit of the machine, but instead by the material itself in conjunction with the manner of strip transport conventionally used in previously known apparatuses which exert a (albeit low) tension and/or thrust on the strip. While the thus produced low expansions and compressions were harmless because of the plasticity of the strip, it was noticed here that the elastoplastic spacer strip on the basis of polyurethane has a kind of shape memory, leading to the consequence that the strip which was expanded and/or compressed by the strip transport tries to assume its original length and its original cross section again. This resetting process can extend with decreasing speed over a period of several hours.